Question: Simplify the following expression: $k = \dfrac{r}{5} - \dfrac{r}{2}$
In order to subtract expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $5$ and $2$ $\lcm(5, 2) = 10$ $ k = \dfrac{2}{2} \cdot \dfrac{r}{5} - \dfrac{5}{5} \cdot \dfrac{r}{2} $ $k = \dfrac{2r}{10} - \dfrac{5r}{10}$ $k = \dfrac{2r -5r}{10}$ $k = \dfrac{-3r}{10}$